Straightforward Solvent-Free Heterogeneous Palladium-Catalyzed Synthesis of Arylamines from Nonaromatic Substrates by Dehydrogenative Alkylation

Abstract

Arylamines can be synthesized in good to excellent yields, with selectivity from nonaromatic and easy available substrates as amines and cyclohexanone derivatives. The dehydrogenative alkylation was catalyzed by a heterogeneous and recyclable Pd/C catalyst, without additional solvent. No atmosphere of molecular oxygen was necessary, making the process safer than reported conditions under oxygen. Thus, the reactions were realized in nonaerobic conditions without any additive when starting from α-tetralones. For functionalized cyclohexanones, the addition of an alkene as a hydrogen scavenger was necessary, and the reaction could also be carried out under air. Besides, arylamines were also synthesized from nitro compounds by cross-dehydrogenative arylation under argon atmosphere. From experimental data, the key intermediate in these transformations seems to be an imine that is dehydrogenated to afford the final aromatic product.